The present invention relates to an electromechanical control device usable for piloting a vehicle, such for example as an aircraft.
Generally, the use of electric flight controls on aircraft leads to transferring to the level of the piloting control sticks two essential functions, namely:
the creation of a resistant force (artificial sensation function),
the fixing of the neutral point of this resistant force in a given position of the course of the control stick (trim function).
In mechanical control devices, these functions are the most often provided by a device placed in parallel across the control gear (trim and force sensation actuator).
Of course, these same functions are to be provided, generally with different characteristics, along the two axes (longitudinal and lateral) of each control stick, whose positions measured by sensors form the piloting orders whether by position or speed control (or integral control).
Furthermore, to take external conditions into account (e.g. the speed) these control devices must comprise means for varying in flight some characteristics of the force law applied to the control stick so as to obtain the most appropriate feeling of resistant force.
The electric control devices used on aircraft more particularly comprise:
a piloting control stick one end of which is provided with a plurality of control knobs ("trim Christmas tree", declutching and priority) and the other end of which is articulated to a support by means of an articulation device with two degrees of freedom, which therefore has two output axes corresponding respectively to rolling and pitching;
a detection assembly comprising one or more position sensors associated with each of these axes;
two electromechanisms adapted so as to oppose to the movements of the control stick a given resistant force (resilient or viscous), these two electromechanisms being usually connected to the roll and pitch axes, either directly or via a transmission device; and
an electronic circuit for controlling the assembly which receives orders from a computer and transmits useful information thereto.
Like the above mentioned mechanical control devices, these electric control devices must be designed so as to guarantee a maximum of safety, particularly by limiting the non catastrophic breakdowns (degraded operation) and preventing catastrophic breakdowns.
Thus, in electric control devices of the type described above, the safety means against the risks of jamming or defective operation of the electromechanisms serving for generating the desired force law, generally comprise a clutch mounted in the transmission device connecting the control stick to each of these electromechanisms, this clutch in particular makes it possible to release the control stick on reception of a control signal emitted following the detection of an anomaly present at the level of the electromechanism and of the electronic circuits which are associated therewith.
It has however proved that such safety devices remain imperfect and do not allow all the operating anomalies to be palliated, to which a control device may be susceptible. Such is the case particularly when the following occur:
jamming of the transmission device associated with an electromechanism (including mechanical jamming at the level of the clutch),
erroneous operation of the control and servo-control electronic circuits for the electromechanisms,
a defect of the circuit controlling the clutch.
The object of the invention is then more particularly to overcome the risks engendered by such anomalies.